Method and system for establishing a power feed to systems during operation

ABSTRACT

A method of adding a power feed to electrical systems includes coupling a set of input lines to a power source such that the input lines are connected to at least one phase of AC power from the power source, and coupling a set of backfeed lines to an output receptacle in a power distribution unit. The output receptacle may be connected in parallel with at least one other output receptacle that is supplying primary power to systems in the data center. The set of backfeed lines and the set of input lines may be tested to determine a match between a pair of lines in the set of backfeed lines and a pair of lines in the set of input lines. Determining the match may include matching the phase of the pair of backfeed lines with the phase of the pair of input lines.

This application is a continuation of U.S. application Ser. No.12/892,750, filed Sep. 28, 2010, now U.S. Pat. No. 8,686,594, which ishereby incorporated by reference in its entirety.

BACKGROUND

Organizations such as on-line retailers, Internet service providers,search providers, financial institutions, universities, and othercomputing-intensive organizations often conduct computer operations fromlarge scale computing facilities. Such computing facilities house andaccommodate a large amount of server, network, and computer equipment toprocess, store, and exchange data as needed to carry out anorganization's operations. Typically, a computer room of a computingfacility includes many server racks. Each server rack, in turn, includesmany servers and associated computer equipment.

Because the computer room of a computing facility may contain a largenumber of servers, a large amount of electrical power may be required tooperate the facility. In addition, the electrical power is distributedto a large number of locations spread throughout the computer room(e.g., many racks spaced from one another, and many servers in eachrack). Usually, a facility receives a power feed at a relatively highvoltage. This power feed is stepped down to a lower voltage (e.g.,110V). A network of cabling, bus bars, power connectors, and powerdistribution units, is used to deliver the power at the lower voltage tonumerous specific components in the facility.

Primary power systems for computer systems in operation typically needto be maintained or reconfigured from time to time. Some data centers,for example, have “single threaded” distribution via the electricalpower supply to the floor and/or to the rack, and in which maintenancecan only be performed when the components using power in the datacenter, such as servers, are shut-off. The down-time associated withmaintenance and reconfiguration of primary power systems in a datacenter may result in a significant loss in computing resources. In somecritical systems such as hospital equipment and security systems,down-time may result in significant disruption and, in some cases,adversely affect health and safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one embodiment of a data centerincluding a backfeed unit that may be used to establish a power feed forcomputer systems in the data center.

FIG. 2A-E are schematic diagrams illustrating one embodiment ofestablishing a backfeed to a rack power distribution unit.

FIG. 3 illustrates one embodiment of adding a power feed to computersystems in a data center and performing reconfiguration or maintenanceoperations while the computer systems remain in operation.

FIG. 4 is a schematic diagram illustrating one embodiment of a feedsystem that may be used to provide a back feed.

FIG. 5 illustrates a front panel view of one embodiment of a backfeedcontrol unit.

FIG. 6 is a schematic diagram illustrating input, master control, andoutput portions of a backfeed control unit according to one embodiment.

FIG. 7 is a schematic diagram illustrating supply pre-return check inletand load pre-return check socket portions of a backfeed control unitaccording to one embodiment.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims. The headings used herein are for organizational purposes onlyand are not meant to be used to limit the scope of the description orthe claims. As used throughout this application, the word “may” is usedin a permissive sense (i.e., meaning having the potential to), ratherthan the mandatory sense (i.e., meaning must). Similarly, the words“include,” “including,” and “includes” mean including, but not limitedto.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments of methods and systems for establishing feeds toelectrical systems, such as computer systems in a data center, aredisclosed. According to one embodiment, a method of adding a power feedto systems while the systems are in operation includes coupling a set ofinput lines to a power source such that the input lines are connected toat least one phase of AC power from the power source, and coupling a setof backfeed lines to an output receptacle in a power distribution unit.The output receptacle may be connected in parallel with other outputreceptacles on the power distribution unit that are supplying primarypower to systems in the data center. The set of backfeed lines and theset of input lines may be tested to determine a match between a pair oflines in the set of backfeed lines and a pair of lines in the set ofinput lines. Determining the match may include matching the phase of thepair of backfeed lines with the phase of the pair of input lines. Thepair of backfeed lines may be coupled to the matching pair of inputlines while primary power is maintained to the systems and the systemsare operating.

According to one embodiment, a method of maintaining electrical power tosystems in operation during reconfiguration or maintenance of a powerdistribution system for the systems includes coupling a set of inputlines to a power source such that the input lines are connected to atleast one phase of AC power from the power source, and coupling a set offeed lines to a power distribution unit that is supplying primary powerto one or more systems in the data center. The set of feed lines and theset of input lines may be tested to determine a match between a pair oflines in the set of feed lines and a pair of lines in the set of inputlines. The pair of feed lines may be coupled to the matching pair ofinput lines while primary power is maintained to the systems and thesystems are operating. Primary power may be disconnected or disabled atone or more points in the primary power chain.

According to one embodiment, a system for supplying power duringreconfiguration or maintenance of a primary power system includes a feedcable including a set of feed lines, an input cable including a set ofinput lines, a synchronization system, and a coupling system. The set ofinput lines may couple with a power source. The set of feed lines maycouple with an output receptacle of a power distribution unit. Thesynchronization system can be used to test lines of the feed cable andlines of the input cable to establish a match of phase and polaritybetween a pair of lines in the set of feed lines and a pair of lines inthe set of input lines. The coupling system may be used to couple a pairof feed lines to a matching pair of input lines.

According to one embodiment, a system for supplying power duringreconfiguration or maintenance of a primary power system includes a setof input lines, a phase selection panel, and a set of feed lines. Theset of input lines can supply power in at least two phases from a sourcepower supply. The phase selection panel includes two or more receptaclescoupled to the set of input lines. The receptacles can supply power fromthe source power supply in different phases and different polarities.The set of feed lines can supply power from the phase selection panel toelectrical loads.

As used herein, “computer room” means a room of a building in whichcomputer systems, such as rack-mounted servers, are operated.

As used herein, “data center” includes any facility or portion of afacility in which computer operations are carried out. A data center mayinclude servers dedicated to specific functions or serving multiplefunctions. Examples of computer operations include informationprocessing, communications, simulations, and operational control.

As used herein, “operating power” means power that can be used by one ormore computer system components. Operating power may be stepped down ina power distribution unit or in elements downstream from the powerdistribution units. For example, a server power supply may step downoperating power voltages (and rectify alternating current to directcurrent).

As used herein, a “match”, in the context of matching sets of powerlines, means that the characteristics between the sets of power linesare similar to one another within acceptable limits. A match does notrequire that the measurements of the two items be precisely equal. Insome embodiments, the acceptable variance levels for a match arepredetermined. For example, in one embodiment, for a voltage levelmatch, an input power line may be predetermined to match a feed line ifthe difference in measured voltage between the two lines is 7 volts orless. Various characteristics, such as voltage, waveform, etc. may beused as criteria to determine a match.

As used herein, a “cable” includes any cable, conduit, or line thatcarries one or more conductors and that is flexible over at least aportion of its length. A cable may include a connector portion, such asa plug, at one or more of its ends.

As used herein, “power distribution unit” means any device, module,component, or combination thereof, that can be used to distributeelectrical power. The elements of a power distribution unit may beembodied within a single component or assembly (such as a transformerand a rack power distribution unit housed in a common enclosure), or maybe distributed among two or more components or assemblies (such as atransformer and a rack power distribution unit each housed in separateenclosure, and associated cables, etc.). A power distribution unit mayinclude a transformer, power monitoring, fault detection, isolation.

As used herein, “primary power” means any power that can be supplied toan electrical load, for example, during normal operating conditions.

As used herein, “floor power distribution unit” refers to a powerdistribution unit that can distribute electrical power to variouscomponents in a computer room. A power distribution unit may be housedin an enclosure, such as a cabinet.

As used herein, “rack power distribution unit” refers to a powerdistribution unit that can be used to distribute electrical power tovarious components in a rack. A rack power distribution may includevarious components and elements, including wiring, bus bars, connectors,and circuit breakers.

As used herein, “remote power panel” means any panel, device, module,component, or combination thereof, that can be used to transfer ordistribute electrical power from one or more input conductors to one ormore output conductors. In certain embodiments, a remote power panelincludes main lug only (“MLO”) panel conductors. A remote power panelmay be housed in an enclosure, such as a cabinet.

As used herein, “reserve power” means power that can be supplied to anelectrical load upon the failure of, or as a substitute for, primarypower to the load.

As used herein, a “secondary feed” refers to any feed that suppliespower that is separate from a primary power system for at least aportion of a primary power chain. As used herein, a “tertiary feed”refers to any feed that supplies power that is separate from two powersystems (such as a primary power system and a reserve power system) forat least a portion of the two power system chains. In some embodiments,a secondary power feed or tertiary feed may be completely independent ofthe primary power distribution system. In some embodiments, however, asecondary feed or tertiary feed is not completely independent of theprimary power distribution system. For example, both the primary powerdistribution system and a secondary feed may both receive power from thesame utility feed, the same step-down transformer (for example, aprimary-side transformer), the same uninterruptible power supply (forexample, a primary-side), etc.

As used herein, “source power” includes power from any source, includingbut not limited to power received from a utility feed. In certainembodiments, “source power” may be received from the output of atransformer.

As used herein, “computer system” includes any of various computersystems or components thereof. One example of a computer system is arack-mounted server. As used herein, the term computer is not limited tojust those integrated circuits referred to in the art as a computer, butbroadly refers to a processor, a server, a microcontroller, amicrocomputer, a programmable logic controller (PLC), an applicationspecific integrated circuit, and other programmable circuits, and theseterms are used interchangeably herein. In the various embodiments,memory may include, but is not limited to, a computer-readable medium,such as a random access memory (RAM). Alternatively, a compact disc-readonly memory (CD-ROM), a magneto-optical disk (MOD), and/or a digitalversatile disc (DVD) may also be used. Also, additional input channelsmay include computer peripherals associated with an operator interfacesuch as a mouse and a keyboard. Alternatively, other computerperipherals may also be used that may include, for example, a scanner.Furthermore, in the some embodiments, additional output channels mayinclude an operator interface monitor and/or a printer.

In some embodiments, a power feed is established to electrical systemswhile systems are live. Systems receiving power from an added feed maybe of various types. Examples include hospital equipment, utilitysystems, security systems, military systems, telecommunications systems,or electronic commerce systems. In certain embodiments, an additionalfeed is provided to a critical system, such as a life support system. Insome embodiments, the systems are computer systems in a data center. Anadditional power feed may allow the primary power system to betemporarily taken off-line for reconfiguration or maintenance of, forexample, the primary power system. In some embodiments, the feed isaccomplished by paralleling a primary power distribution system over aportion of a power distribution chain.

In some embodiments, a backfeed system is used to establish a feed toelectrical systems. FIG. 1 is a block diagram illustrating oneembodiment of a data center including a backfeed system that may be usedto establish a secondary power feed for computer systems in the datacenter. Data center 50 includes rack systems 51 and primary power side100. Primary power side 100 includes transformer 102, generators 104,and switchgear 105, and primary power systems 106. Rack systems 51include racks 52. Sets of computer systems 54 in racks 52 may performcomputing operations in data center 50. Computer systems 54 may be, forexample, servers in a server room of data center 50. Computer systems 54in racks 52 may each receive power from one of primary power systems106. In one embodiment, each of primary power systems 106 correspondsto, and provides power to, the servers in one room in data center 50. Inone embodiment, each of primary power systems 106 corresponds to, andprovides power to, one of rack systems 51 in data center 50.

Primary power systems 106 each include UPS 110 and floor powerdistribution unit 112. Floor power distribution unit 112 provides powerto various of rack systems 51. In some embodiments, floor powerdistribution unit 112 includes a transformer that transforms the voltagefrom switchgear 105. Each of rack systems 51 may include a rack powerdistribution unit 56. Rack power distribution units 56 may distributepower to computer systems 54.

Transformer 102 is coupled to a utility feed. The utility feed may be amedium voltage feed. In certain embodiments, the utility feed is at avoltage of about 13.5 kilovolts or 12.8 kilovolts at a frequency ofabout 60 Hz. Generators 104 may provide power to primary power systems106 in the event of a failure of utility power to transformer 102. Inone embodiment, one of generators 104 provides back-up power for each ofprimary power systems 106. UPS 110 may provide uninterrupted power toracks 52 in the event of a power failure upstream from UPS 110.

For illustrative purposes, three primary power systems are shown in FIG.1 (for clarity, details of only the front primary power system 106 areshown). The number of primary power systems 106 on primary power side100 may vary, however. In certain embodiments, a primary power side mayinclude only one primary power system. In addition, the number of powerdistribution units, UPSs, switchgear apparatus may vary from embodimentto embodiment (and, within a given embodiment, from system to system).In some embodiments, primary power system 106 includes many floor powerdistribution units 112. As another example, a primary power system mayhave one UPS that can supply power to many floor power distributionunits.

Data center 50 includes backfeed unit 120. Backfeed system 120 may beused to provide a secondary power feed to rack systems 51. The secondarypower feed may be provided, for example, during reconfiguration ormaintenance of primary power systems 106. Backfeed system 120 includessynchronization system 122, input cable 124, and output cables 126.Synchronization system 122 includes synchronization receptacle panel130, paralleling panel 132, backfeed unit input cable 134, and meters136. Input cable 124 includes input coupling device 138. Backfeed cables126 include backfeed plugs 140.

Meters 136 may be used to measure power characteristics, such asvoltage, line voltage, wave form, frequency, phase sequence, and phaseangle, within synchronization system 122, or on the input and/or outputsides of backfeed system 120. In some embodiments, one or more of meters136 are integrated into an enclosure for backfeed system 120. In otherembodiments, one or more of meters 136 is a stand alone measurementdevice, such as a stand-alone oscilloscope.

In some embodiments, a backfeed unit supplies a secondary power bybackfeeding one or more receptacles in a power distribution unit. Insome embodiments, a backfeed unit is used to create a secondary powerfeed by tapping into a floor power distribution unit. FIG. 2A-C areschematic diagrams illustrating one embodiment of establishing abackfeed to a rack power distribution unit. FIG. 2A illustrates oneembodiment of a portion of data center including a backfeed unit for arack power distribution unit. Data center 150 includes computer systems54 in rack 52, primary power system 106, and backfeed system 120.Primary power system 106 includes UPS 110, floor power distribution unit112, and rack power distribution unit 56. Rack power distribution unit56 may supply power to computer systems 54. Primary power distributionsystem 106 may be similar to that described above relative to FIG. 1.UPS 110 may receive power from a transformer, such as transformer 102described above relative to FIG. 1.

UPS may receive three-phase power from a transformer, such astransformer 102 illustrated in FIG. 1. UPS 110 may supply three-phasepower to floor power distribution unit 112 through lines 152. In FIG.2A, each of the three lines is designated A, B, or C to indicate one ofthe three phases of power received from UPS 110.

Floor power distribution unit 112 includes floor PDU receptacles 154.Floor PDU receptacles 154 may be used to supply power to various racksin data center 150. In one embodiment, floor PDU receptacles 154 areNEMA L6-30R type. Each of the various receptacles on floor powerdistribution unit 112 may carry two phase lines and one ground. In FIG.2A, each of the six receptacles is in indicated with one of the sixphase combinations, namely, AB, BC, AC, BA, CB, or CA.

In the embodiment shown in FIG. 2A, combinations for illustrativepurposes, floor PDU receptacles 154 are shown on floor powerdistribution unit 112 for only two of the six phase combinations. Afloor power distribution unit may, however, have any number ofreceptacles for each phase combination. In some embodiments, a floordistribution unit may have one receptacle for each of the six phasecombinations. In some embodiments, a floor distribution unit may havetwo or more receptacles for each of the six phase combinations. In someembodiments, a floor power distribution may have outputs for only someof the phase combinations (for example, AB, BC, and AC only). In certainembodiments, a floor distribution unit may receive and/or distributetwo-phase power. In certain embodiments, a floor distribution unit mayreceive and/or distribute a single phase (for example, hot, neutral, andground).

Rack power distribution unit 114 includes rack PDU receptacles 156. Inone embodiment, rack PDU receptacles 156 are IEC 60320 C20 receptacles.All of rack PDU receptacles 156 may be wired in parallel with oneanother. In typical operation of data center 150, any or all of rack PDUreceptacles 156 may be used to supply power to computer systems in rack54. In the embodiment shown in FIG. 2A, the leftmost two of rack PDUreceptacles are used to provide power to computer systems 54 in rack 52.

Backfeed system 120 includes synchronization receptacle panel 130.Synchronization panel receptacle panel 130 includes synchronizationreceptacles 160. Backfeed unit input 134 includes phase selection plug162.

FIG. 2B illustrates a backfeed connection to receptacles on a rack powerdistribution unit. Backfeed plugs 140 of backfeed cables 126 are coupledto two of rack PDU receptacles 156 on rack power distribution unit 114.Although in the embodiment shown in FIG. 2B, power is backfed to tworeceptacles in the rack PDU, power may in various embodiments be fed toany number of receptacles in a rack PDU. The number of backfeedreceptacles may depend on amount of current required by the electricalloads connected to the rack PDU. In certain embodiments, each ofmultiple rack PDUs in a data center may have a backfeed into only onereceptacle.

In some embodiments, input coupling device 138 is a 3-pole circuitbreaker. In certain embodiments, input coupling device 138 is a 3-poleminiature circuit breaker (MCB). Coupling device 138 may be installed ina breaker panel in floor power distribution unit 112. Each pole of thethree poles may be connected to one of the three-phases, namely, A, B,or C.

Once backfeed cables 126 have been coupled to rack power distributionunit 114 to be backfed and floor power distribution unit 112 has beencoupled to a power source (in this case, floor power distribution unit112), the power on the lines of input cables 124 and backfeed cables 126may be tested for synchronization. In some embodiments, synchronizationis as further described below relative to FIG. 3. In some embodiments,one or more of meters 136 are used to test any or all of the followingparameters: wave form, line voltage, frequency, phase sequence, andphase angle. In addition, stability of various parameters may beassessed. Synchronization may include establishing a match between thepair of backfeed lines 164 in backfeed cable 126 and a combination ofinput lines 166 from floor power distribution unit 112. For example, forthe embodiment shown in FIGS. 2A-2C, by probing backfeed lines 164 andinput power lines 166 (for example, on the load side of coupling device138), it may be determined the voltage and phasing on backfeed lines inis a BC phase combination. The power characteristics, such as linevoltage, frequency, etc. of the BC input lines may be measured andcompared to the power characteristics of the feed lines. Based on thesynchronization test, a user may couple backfeed unit input cable 134 onparalleling panel 132 to receptacle BC on synchronization receptaclepanel 130, as shown in FIG. 2C. Coupling of phase selection cable 134 toreceptacle BC on phase synchronization receptacle panel 132 mayestablish a backfeed to computer systems 54 in rack 52. In thearrangement shown in FIG. 2C, computer systems 54 may receive a parallelpower feed, one feed from floor PDU receptacle 154, and another from thebackfeed into rack PDU receptacles 156.

In some embodiments, reconfiguration or maintenance operations areperformed under live conditions (for example, while maintaining serversin a powered up state and performing computing operations using theservers). In one embodiment, computer systems in a rack are maintainedlive while an automatic transfer switch is installed between a floorpower distribution unit and a rack power distribution unit for thecomputer systems. The installed automatic transfer switch may be used,for example, to switch to a reserve power system. FIGS. 2D-2E illustrateone embodiment of installing an automatic transfer switch for reservepower system for a rack system in a data center. The installation may becarried out in a “live” environment in which the computer systems in therack remain in operation. As reflected in FIG. 2D, a backfeed has beenestablished as described in FIGS. 2A-2C. In addition, power plug 170 ofrack power distribution unit 114 has been disconnected from floor powerdistribution unit 112. Computer systems 54 continue to receive powerthrough the feed from backfeed unit 120.

As reflected in FIG. 2E, automatic transfer switch 174 may be installedbetween floor power distribution unit 112 and rack power distributionunit 114. Power plug 170 of rack power distribution unit 114 may becoupled to the output receptacle 176 of automatic transfer switch 174.Input power plug 178A of automatic transfer switch 174 (the “A” side ofthe automatic transfer switch) may be connected to floor PDU receptacle154 in floor power distribution unit 112. (Input power plug 178A may beinstalled into the same receptacle that input power plug 170 of rackpower distribution 114 was previously installed in.) At this point,primary power may be reestablished from floor PDU receptacle 154.Backfeed system 120 may be disconnected from rack power distributionunit 114.

As reflected in FIG. 2E, input power plug 178B of automatic transferswitch 174 (the “B” side of the automatic transfer switch) may beconnected to reserve PDU 180, which may be part of a reserve powersystem. The reserve power system may remain coupled to provide back-uppower to computer systems 54 in rack 52.

In some embodiments, a reserve power system provides reserve power forall of the computer systems 54 supplied by primary power systems 106. Insome embodiments, the reserve power system is powered up at all timesduring operation of data center 50. The reserve power system may bepassive until a failure of one or more components of primary power side100, at which time the reserve power system may become active.

If automatic transfer switches are to be installed in additional racksystems, backfeed system 120 may be used to provide a backfeed to suchracks by repeating the procedure as described above.

In various embodiments, a backfeed to a power distribution is suppliedby tapping an element in a power chain that is upstream from backfedpower distribution unit. As illustrated in the embodiments shown in FIG.2A-2E, for example, a backfeed to a rack power distribution unit 56 maybe supplied from a floor power distribution unit 112. Floor powerdistribution unit 112 is upstream from, and supplies power to, rackpower distribution unit 56. In another embodiment, a backfeed may besupplied from an uninterruptible power supply in the primary powersystem (such as UPS 110 of primary power system 100 shown in FIG. 1. Abackfeed may be supplied from any power source, however. For example, abackfeed may be supplied from a floor power distribution unit in a datacenter other than the floor power distribution unit 114, from a reservepower system, or a source external to the data center.

In some embodiments, a power feed is added to systems in a data centerwhile the systems are in operation. The power feed may be accomplished,in some embodiments, by backfeeding a power distribution unit in thedata center. FIG. 3 illustrates one embodiment of adding a secondarypower feed to computer systems in a rack in a data center and performingreconfiguration or maintenance operations while the computer systemsremain in operation. In some embodiments, reconfiguration or maintenanceoperations may be repeated for various racks in a data center all theway to the rack PDU level without removing power from the components inthe racks.

As operations may be performed “hot”, electrical safety precautions maybe utilized, which may include ensuring that: (1) all electrical safetyprocedures are followed; (2) personal protective equipment is used; (3)proper change management/configuration management is in place,identifying the specific rack(s) being back-fed and notifying the properpersonnel; and (4) the primary feed to the server rack(s) has noabnormal conditions that would jeopardize the rack during a secondaryfeed process. For example, power characteristics such as voltagedeviation, frequency deviation, and phase deviation may be determined tobe within acceptable ranges, for example, within plus or minus 5%.Throughout the process, multiple connectors may be energized since anadditional power source is being introduced. Precautions may be takenthat these connectors are carefully handled, and properly insulated.

At 500, a set of input lines is coupled to a power source such that theinput lines are connected to alternating current (“AC”) power from apower source. In one embodiment, the power source is another floor powerdistribution unit in a primary power distribution system (for example,if space is not available for a circuit breaker in the primary floor PDUfeeding the rack PDU). In some embodiments, the criteria for using a PDUas a power source for a feed include the following two conditions: (1)the alternate PDU is fed from the same UPS as the source PDU; and (2)the voltages on matching phases are within a predetermined variance ofeach other (and same frequency). In one embodiment, the predeterminedvariance is 7 volts AC or less.

In some embodiments, a backfeed system such as described herein relativeto FIG. 1 may be used to establish a feed to a rack. In someembodiments, the backfeed unit includes a synchronization receptaclepanel and a paralleling panel, such as paralleling panel 132 describedabove relative to FIG. 1 and/or described below relative to FIG. 4. Theparalleling panel may provide a path from the synchronization receptaclepanel to the power distribution unit to be back fed. In otherembodiments, a special cable may be used to provide the back-feed fromthe synchronization receptacle panel to the power distribution unit tobe backfed. In one embodiment, the end of the cable that couples with arack PDU is a male C19 and the end of the cable that couples with thesynchronization panel is a NEMA L6-30P. Other connectors and cablearrangements may be used in various embodiments. In certain embodiments,a cable may have a Y-arrangement, utilizing two other male IEC 60320 C19connectors at one end, or two IEC 60320 C13 connectors at one end.

In one embodiment, a 3-pole breaker is installed in a floor PDU toprovide a backfeed to a rack PDU. Enough cable may be left exposed onthe load side of the breaker to be able to measure the current on eachphase with a tong ammeter or a grip ammeter. Once installed, the 3-polebreaker may be shut.

Equipment for establishing a feed, such as backfeed system 120 describedabove relative to FIG. 1, may be staged in any suitable location. In oneembodiment, the backfeed unit is positioned at the end of row to preventinterference with other server racks. In certain embodiments, testand/or feed equipment may be mounted on a cart.

At 502, a set of secondary feed lines is coupled to a power distributionunit that is supplying primary power to one or more systems in the datacenter. The secondary line feed may be into a rack-level PDU thatsupplies power to a rack (for example, a 5 KVA 208 V×24 Amp PDU). Insome embodiments, the secondary lines are coupled as a backfeed to oneor more output receptacles in a power distribution unit (such as anon-active C19 connector). The output receptacles may be connected inparallel with output receptacles that are supplying primary power to oneor more systems in the data center. The phasing on the circuit on therack to be back-fed (for example, A-B, B-C, or C-A) may be identified.Any number open output receptacles may be backfed. The number ofreceptacles may be based, for example, on load requirements of thesystems receiving power from the rack power distribution unit.

In some embodiments, the backfeed may be synchronized with power fromthe power source. At 504, the secondary feed lines and input lines aretested to determine a match between a pair of lines in the set ofsecondary feed lines and a pair of lines in the set of input lines tomatch the phase of a pair of secondary feed lines with the phase of thea pair of input lines. Matching may include determining characteristicsincluding wave form, line voltage, frequency, phase sequence, and phaseangle. In some embodiments, an oscilloscope is used for testing ofvarious characteristics.

Using a meter, the potential difference between the feed lines and theinput lines may be checked to ensure that the phases line up. In someembodiments, one or more meters may be built into a synchronizationsystem for secondary feed. In certain embodiments, the meter may be amulti-meter. If the phases are reversed, then an alternate receptaclemay be used for the same phase combination (for example, BA instead ofAB).

In some embodiments, the power source for a secondary feed may be a PDUother than the primary floor PDU for the circuit in the rack. In suchembodiments, a maximum variation may be established for the potential.In one embodiment, the potentials allowed to differ by no more than of 7VAC. In another embodiment, the potential is allowed to differ by nomore than 5%. In some embodiments, phase integrity may be verified bytwo electricians.

At 506, a pair of secondary feed lines is coupled to the matching inputlines while primary power is maintained to the systems and the systemsare operating, which may establish a secondary feed to the systems.Verification may be made that the computer systems being fed by thesecondary feed are operating properly. In addition, the load bearingcapacity of the feed may be assessed, for example, via an amprobe on theload side of a 3-pole breaker coupled to the power source.

At 508, primary power is disabled or disconnected at a point in theprimary power chain.

At 510, reconfiguration or maintenance operations may be performed onthe power distribution system while primary power is disconnected ordisabled and the secondary feed is supplying power to the systems. Forexample, as described above relative to FIGS. 2D-2E, a backfeed may beused to carry out a live power cut-over during installation of an ATS atthe rack level. After installation, the load bearing capacity of the PDUcircuit through the ATS may be verified, for example, using an amprobeon the load side of the circuit.

At 512, after performing the at least one reconfiguration or maintenanceoperation, the primary power system may be reconnected or re-enabled.

At 514, the secondary feed may be disconnected from the powerdistribution unit being fed. Tests may be performed to verify that therack is operating properly, and that no alarms are present at the PDU orUPS.

At 516, a determination is made whether reconfiguration or maintenanceprocedures are needed for additional racks. If so, all or part of theprocedure may be applied to additional racks at 518. In someembodiments, the input feed lines may remain connected to the same powersource while reconfiguration or maintenance is performed on severalracks in a data center. In some embodiments, a secondary feed may beestablished to numerous PDUs. For each PDU, tests may be performed toestablish the appropriate phase and whether a match exists beforeconnecting the input lines to a backfeed line for the PDU. For example,the rack PDU for a one rack may have power with an AB phase combination,the rack PDU for another rack may have power with a CB phasecombination, and so on. In some cases, a single rack PDU may have setsof receptacles on different phase combinations. Thus, in someembodiments, a backfeed procedure may be performed multiple times on asingle rack PDU (for example, once for each phase combination on therack PDU from which power is being supplied).

In some embodiments, input lines may be switched to a different powersource (such as a different floor PDU) when reconfiguration ormaintenance is performed for different racks.

When no more circuits will be back-fed, the breaker coupling the inputlines to power source may be opened and removed from the power source at520.

Although in the examples described above, the secondary feed or backfeedwas established by feeding into a power distribution unit, in certainembodiments, a secondary or tertiary feed may be established by feedinginto other elements in a power distribution system. In certainembodiments, a secondary feed is established by backfeeding into aremote power panel.

Although in the examples described above, a secondary feed is made intoa rack-level PDU, a secondary power feed may in various embodiments besupplied to any component in a system. In one embodiment, a backfeed isestablished into output receptacles of a floor PDU, such as floor powerdistribution unit 114 described above relative to FIG. 1. The powersource may come from any source, such as different floor PDU, a UPS, orother system. A floor PDU back feed may be established, for example, toreplace a circuit breaker in the floor PDU.

FIG. 4 is a schematic diagram illustrating one embodiment of a feedsystem that may be used to provide a back feed. Feed system 800 includesreceptacle panel 804 and paralleling panel 805. Feed system 800 mayreceive power from donor PDU 801. Feed system 800 may be coupled todonor PDU 801 by way of MCB 802. In one embodiment, MCB is a 30 amp,3-pole D curve MCB.

Receptacle panel 804 includes isolator 806 and receptacles 808. In oneembodiment, isolator 806 is door mounted (lockable) paralleling isolatorrated AC23, 63 amps, with test points provided on both sides of theisolator. One receptacle 808 may be provided for each of the variousphase combinations from donor PDU 801.

The components of receptacle panel 804 may be housed in an enclosure.The components of paralleling panel 805 may be housed in a separateenclosure. In certain embodiments, each of receptacles 808 is housed ina separate enclosure, as illustrated by boxes 809.

Paralleling panel 805 includes plug 810, cable 811, receptacle 814,isolator 816, ammeter 818, terminal rails 820, isolators 822, and flexcords 824. Isolator 816 may be a door mounted (lockable) parallelingisolator rated AC23, 63 amps, with test points provided on both sides ofthe isolator. Isolators 822 may be double pole, door mounted (lockable),rated at 20 amps.

Plug 810 is provided at the end of cable 811. Receptacle 814 may providea safe housing for plug 810. In one embodiment, plug 810 is NEMA L6-30Pand receptacles 808 and 814 are NEMA L6-30R.

Flex cords 824 may be glanded to the enclosure of paralleling panel 805or may be connected by plug and receptacle. Cable glands may be includedto provide sealing and/or strain relief for flex cords 824 where flexcords 824 pass into the enclosure of paralleling panel 805. Flex cords824 may be routed to rack PDU 826.

Flex cords 824 may be coupled in receptacles 827 of rack PDU 826. RackPDU 826 may include plug 829. Receptacle 828 may be provided for safehousing of input plug 829.

FIG. 5 illustrates a front panel view of one embodiment of a backfeedcontrol unit. A backfeed control unit may be used, for example, as aparalleling panel in the backfeed unit described above relative toFIG. 1. Backfeed control unit 860 includes front panel 864 and inputcable 862. Input cable 862 may couple with a power source, eitherdirectly or through an intermediate system such as receptacle panel 804described above relative to FIG. 4. Master control 866 and outputs 868are provided on front panel 864. Master control 866 includes masterswitch 870, test points 872, ammeter 874, and indicator lamps 876. Eachof outputs 868 includes output receptacle 878, test points 880, ammeter882, and switch 884.

Input cable 862 includes plug 863. In one embodiment, plug 863 is a IEC60309 2P+NE, 32 A plug. In another embodiment, plug 863 is a L6-30Pplug.

Power may be routed from input cable 862 to each of outputs 868. Ammeter874 may provide a visual indicator of a current level in input cable862. Ammeters 882 may provide a visual indication of a current level ineach of outputs 868. Switches 870 and 884 maybe used to control poweroutputs 868.

Backfeed control unit 860 includes supply pre-return check inlet 890 andload pre-return check socket 892. Supply pre-return check inlet 890includes test points 894. Load pre-return check socket 892 includes testpoints 896.

FIG. 6 is a schematic diagram illustrating the input cable 862, mastercontrol 866, and output 868 portions of backfeed control unit 860according to one embodiment. FIG. 7 is a schematic diagram illustratingthe supply pre-return check inlet 890 and load pre-return check socket892 portions of backfeed control unit 860 according to one embodiment.In one embodiment, supply pre-return check inlet 890 is a IEC 603092P+NE, 32 A male connector portion and load pre-return check socket 892is a IEC 60309 2P+NE, 32 A receptacle.

In various embodiments described above, a synchronization systemprovides for manual testing for synchronization between a power sourceand a power distribution unit to be fed. In certain embodiments,however, testing to establish synchronization may be performedautomatically or semi-automatically, for example, by a processor in asynchronization system. In addition, in some embodiments, coupling of apower source (via, for example, a set of input lines) with a powerdistribution unit to be fed (via, for example, a set of secondary feedlines to the PDU) may be performed automatically or semi-automatically,for example, by a processor in a synchronization system.

In various embodiments described above, a feed system is wired toprovide any combination of phases from a three-phase power source. Afeed system may, however, provide other types of power (for example,two-phase, single phase). In one embodiment, a secondary feed systemreceives two-phase power from a power source and allows synchronizationfor any combination of phases of the two-phase power. In one embodiment,a secondary feed system receives single-phase power (for example, onehot and one neutral) from a power source and allows synchronization withany phase and neutral of a poly-phase system.

In various embodiments described above, a secondary feed is establishedfor systems during operation of the systems. In certain embodiments,however, some or all of the systems in a data center may be taken out ofoperation during establishment of a secondary feed.

Although in some embodiments described herein, an additional feed is asecondary feed connected in parallel to a single primary feed, powerfeeds may, in various embodiments, be added to systems having any numberof existing feeds. Thus, an additional power feed may be a secondarypower feed, a tertiary power feed (for example, a feed to a systemreceiving power from two existing power systems), etc.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A method, comprising: determining a match betweenat least one pair of input lines coupled to a power source and at leastone pair of backfeed lines coupled to an output receptacle in a powerdistribution unit that is supplying, via at least one other outputreceptacle, primary power to one or more systems, wherein saiddetermining the match is based at least in part upon a phase of the atleast one pair of backfeed lines and a phase of the at least one pair ofinput lines; and coupling the at least one pair of backfeed lines to thematching at least one pair of input lines, based at least in part upondetermining the match, while primary power is maintained to the systemsand the systems are operating.
 2. The method of claim 1, whereindetermining the match between at least one pair of backfeed lines and atleast one pair of input lines comprises determining a match between awaveform of the at least one pair of input lines and a waveform of theat least one pair of backfeed lines.
 3. The method of claim 1, wherein:the power supplied to the at least one pair of input lines comprisesthree phase power; determining the match between at least one pair ofbackfeed lines and the at least one pair of input lines comprisesdetermining the phase and polarity of the at least one pair of backfeedlines; and coupling the at least one pair of backfeed lines to thematching at least one pair of input lines comprises coupling the atleast one pair of backfeed lines to the at least one pair of input linesthat matches the phase and polarity of the at least one pair of backfeedlines.
 4. The method of claim 1, wherein coupling the at least one pairof backfeed lines to the matching at least one pair of input lines isperformed automatically.
 5. The method of claim 1, further comprisingperforming at least one reconfiguration operation on the powerdistribution system while primary power is disconnected or disabled andthe at least one pair of backfeed lines is supplying power to the one ormore systems.
 6. The method of claim 5, wherein performing the at leastone reconfiguration operation comprises connecting a reserve powersystem to the power distribution system.
 7. The method of claim 5,wherein performing the at least one reconfiguration operation comprisescoupling an automatic transfer switch between a floor power distributionunit and a rack power distribution unit.
 8. The method of claim 1,further comprising performing at least one maintenance operation on thepower distribution system while primary power is disconnected ordisabled and the at least one pair of backfeed lines is supplying powerto the one or more systems.
 9. The method of claim 1, furthercomprising: performing at least one reconfiguration or maintenanceoperation on the power distribution system while primary power isdisconnected or disabled and the at least one pair of backfeed lines issupplying power to the one or more systems; reconnecting or re-enablingprimary power after performing the at least one reconfiguration ormaintenance operation; and disconnecting the at least one pair ofbackfeed lines from the at least one pair of input lines after primarypower has been reconnected or re-enabled.
 10. A system, comprising: aphase selection panel comprising: two or more receptacles configured tobe coupled to a set of input lines configurable to supply power in atleast two phases from a source power supply, wherein each of at leastone of the receptacles is configured to supply power from the sourcepower supply in a different phase or different polarity from at leastone other of the receptacles.
 11. The system of claim 10, wherein: theset of input lines is configurable to supply power in three phases fromthe source power supply; and the phase selection panel comprises atleast one receptacle for each phase combination of the three phase powerin the set of input lines.
 12. The system of claim 10, furthercomprising: a set of feed lines configurable to supply power from thephase selection panel to at least one electrical load; and a feed unitinput cable coupled to the set of feed lines, wherein the feed unitinput cable is configured to plug into at least two of the receptaclesin the phase selection panel to establish a feed from the input lines tothe feed lines.
 13. The system of claim 12, further comprising at leastone meter configurable to test synchronization between lines in the setof feed lines and one or more lines.
 14. A system, comprising: asynchronization system configured to: couple with an output receptacleof a power distribution unit via at least one pair of feed lines, suchthat the at least one pair of feed lines carry power supplied by thepower distribution unit from the output receptacle; couple with a powersource via at least one pair of input lines, such that the at least onepair of input lines carry power supplied by the power source; andestablish a match of phase and polarity between the power carried by theat least one pair of feed lines and the power carried by the at leastone pair of input lines, based at least in part upon testing the feedlines and input lines.
 15. The system of claim 14, wherein thesynchronization system comprises: a coupling system configured to couplethe at least one pair of feed lines to at least one matching pair ofinput lines, based at least in part upon the synchronization systemestablishing the match.
 16. The system of claim 14, wherein the couplingsystem comprises: a phase selection panel comprising two or morereceptacles coupled to the at least one pair of input lines, whereineach of at least one of the receptacles is configured to supply powerfrom the power source in a different phase or different polarity from atleast one other of the receptacles; and a feed unit input cable coupledto at least one of the at least one pair of feed lines, wherein the feedunit input cable is configured to plug into at least two of thereceptacles in the phase selection panel to establish a feed from theinput lines to the feed lines.
 17. The system of claim 14, wherein thesynchronization system comprises a paralleling panel comprising two ormore output receptacles, wherein each of at least two of the outputreceptacles are configured to supply power to at least one of the atleast one pair of feed lines.
 18. The system of claim 17, wherein theparalleling panel comprises at least one switch configured to switchpower in at least one of: at least one of the at least one pair of feedlines, or at least one of the at least one pair of input lines.
 19. Thesystem of claim 14, wherein the synchronization system comprises atleast one meter configurable to test synchronization of the feed lineswith the input lines.